As it is well known in the field of computer science, a virtual machine monitor (VMM) which may be alternatively named as a “hypervisor” or a “virtualization kernel,” is a virtualization software that is logically interposed and interfacing between hardware resources of a computer system and one or more virtual machines VMs executed in the VMM. A virtual machine (VM) which may be alternatively named as a “guest,” is a software abstraction or in other words virtualization of an actual computer system, that can be operated under an operating system like Windows, Unix, Linux, etc. and can support applications running on the operating system. The VMM allocates hardware devices or portions of hardware devices of the computer system like CPUs, hard drives, I/O ports, memory, etc. to the VMs in a form of so called virtual resources. For instance VMM can map hardware disks to virtual disks used for operation of the VMs.
Virtualization architecture of the hardware resources can consist of one or more virtualization layers or levels. For instance, a Linux guest running in the z/VM hypervisor developed by IBM which runs in a PR/SM partition of an IBM System z server is an example of a setup with two layers of virtualization. In general, the virtualization architecture can be quite complex and comprise a lot of virtualization layers.